In the design and manufacture of aircraft, it is generally desirable to minimize the space required by aircraft components. One approach to saving space is to shorten the length of the landing gear before or during retraction into a stowed position in the aircraft. The shortened length of the landing gear may be required by the initial design of an aircraft or may be desired to minimize design changes in future generations of an existing aircraft.
A prior art design for shortening the overall length of a strut during retraction is described in U.S. Pat. No. 5,908,174 to Churchill et al. The patent discloses a shock strut that automatically shrinks the length of an aircraft landing gear strut during the landing gear's retraction into the aircraft. The shock strut includes a hydraulic transfer cylinder that transfers hydraulic fluid into a strut shrink chamber while simultaneously driving pressurized gas from a gas spring chamber of the strut into the hydraulic transfer cylinder. The hydraulic transfer cylinder is physically integrated with a landing gear retract actuator such that a linear motion of a retract actuator effects an equal linear motion of the hydraulic transfer cylinder. In other words, the hydraulic transfer cylinder is mechanically linked to the landing gear retract actuator such that the hydraulic transfer cylinder cannot operate independently from the retract actuator, and thus the extension and shrinking of the landing gear strut is automatically effected during landing gear retraction and deployment. On deployment, a hydraulic lock on the transfer fluid in the strut shrink chamber is removed and the pressurized gas that was transferred to the transfer cylinder drives the transfer fluid from the strut shrink chamber back into the transfer cylinder. As the transfer fluid exits the strut shrink chamber, the pressurized gas returns to the strut from the transfer cylinder and causes the strut to return to its extended length.
Other prior art designs provide a shrink actuator that is independent of the retract actuator but require a heavy and cumbersome mechanical linkage to exert an axial shrinking force on the strut sufficient to overcome the strut's internal pressurized gas bias and cause the strut to shrink. Such designs generally require high hydraulic fluid flow rates that may not be available from the aircraft's high pressure/low flow rate hydraulic system. Such designs may further require a larger landing gear envelope in the fuselage of the aircraft to accommodate the mechanical linkage and the shrink actuator.